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External-Compression Supersonic Inlet Design Code
A computer code named SUPIN has been developed to perform aerodynamic design and analysis
of external-compression, supersonic inlets. The baseline set of inlets include axisymmetric pitot,
two-dimensional single-duct, axisymmetric outward-turning, and two-dimensional bifurcated-duct
inlets. The aerodynamic methods are based on low-fidelity analytical and numerical procedures.
The geometric methods are based on planar geometry elements. SUPIN has three modes of
operation: 1) generate the inlet geometry from a explicit set of geometry information, 2) size and
design the inlet geometry and analyze the aerodynamic performance, and 3) compute the
aerodynamic performance of a specified inlet geometry. The aerodynamic performance quantities
includes inlet flow rates, total pressure recovery, and drag. The geometry output from SUPIN
includes inlet dimensions, cross-sectional areas, coordinates of planar profiles, and surface grids
suitable for input to grid generators for analysis by computational fluid dynamics (CFD) methods.
The input data file for SUPIN and the output file from SUPIN are text (ASCII) files. The surface
grid files are output as formatted Plot3D or stereolithography (STL) files. SUPIN executes in batch
mode and is available as a Microsoft Windows executable and Fortran 95 source code with a
makefile for Linux.
Dr. John W. Slater, NASA Glenn Research Center / Inlet and Nozzle Branch (RTE)
1
National Aeronautics and Space Administration
www.nasa.gov
External-Compression Supersonic Inlet Design Code
2011 Technical Conference
March 15-17, 2011
Cleveland, Ohio
Dr. John W. Slater
NASA Glenn Research Center / Inlet and Nozzle Branch /
Supersonic Cruise Efficiency - Propulsion
Supersonics Project
2
Background
Goal: Develop computational tools to perform aerodynamic design and analysis of
supersonic inlets to determine inlet geometry and performance.
Some key points:
o Supersonic inlet design methods have been developed over the last 60+ years.
o Various computational tools have been developed over the decades (IPAC, InletMOC,
LercInlet, LAPIN) based on analytic, empirical, and computational methods.
o New computational frameworks (Java, Matlab, etc…) and new inlet concepts (stream-
traced, advanced flow control, etc…) have prompted us to re-visit our supersonic inlet
design tools and to develop new tools.
o The tools should perform low-fidelity analysis while also providing geometry for higher-
fidelity, computational fluid dynamics (CFD) analysis.
o This has lead to the Inlet Tools effort of the Supersonic Project.
o Small-scale effort: the work discussed in this presentation has involved one researcher
(John Slater) at ½ full-time employee (FTE) for about 3 years.
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Four Aspects to the Inlet Tools Effort
1. Inlet Tools Electronic Database
• Internet-based eRoom (access is controlled by member account
with userid and password).
• Database stores files submitted by members.
• Database contains PDF files of public-domain papers, reports,
and other literature.
• Location to store data, source code, input and output files.
Aspects of the Inlet Tools Effort
1. Electronic Database
2. Design and Analysis Document
3. Geometry Model
4. Computational Tools
2. Inlet Design and Analysis Documentation
• Documents fundamental aerodynamic design and analysis methods suitable for supersonic inlets.
• Provide background for methods coded into the computational tools.
• Document the inlet geometry model and computational tools.
• The document is in the form of a MS Word document.
3. Inlet Geometry Model
• Describes supersonic inlet geometry in terms of basic parts and key geometric factors.
• Recognizes that some inlet geometry can be constructed from simple, planar entities.
• Provides framework for constructing surfaces for visualization and CFD analysis.
4. Computational Tools
• Implements the inlet geometry model and design and analysis methods into a computer program.
• Various frameworks can be used (Fortran 95, Java, Python, C++, Matlab, etc…)
4
SUPIN (SUPersonic INlet) Design Code
• Incorporates the supersonic inlet geometry model and design and analysis methods.
• Currently capable of design and analysis of external-compression, supersonic inlets (Mach1.6-2.0).
• Written in Fortran 95 on Windows laptop.
• Text-based (ASCII) input data file with blocks and lines of input.
• Text-based (ASCII) output file containing inlet coordinates and performance properties.
• Creates surface and planar CFD grid files (ASCII Plot3d and STL formats).
• Single code with an Windows executable or source code and makefile for Unix / Linux systems.
• Modes of inlet design and analysis:
o Kmode = 1. Generate the inlet geometry from an explicit set of geometry factors and inputs.
o Kmode = 2. Perform design operations to size and generate the geometry of the inlet based on
specified factors and inputs.
o Kmode= 3. Perform aerodynamic analysis of an inlet defined from an explicit set of geometry
factors and inputs.
• Primary inlet performance measures include:
o Flow rates
o Total pressure recovery
o Inlet drag
• Inlet aerodynamics also includes total pressure distortion, stability (buzz), etc…
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Baseline Inlet Shapes
Axisymmetric
Pitot (Ktyp = 1)
Two-Dimensional, Bifurcated
Duct (Ktyp = 4)
Axisymmetric, Outward-
Turning (Ktyp = 3)
Two-Dimensional, Single
Duct (Ktyp = 2)
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Parts of the Inlet Flow Field
Nose
Engine
FaceThroat
External Supersonic
Diffuser
Subsonic
Diffuser
Cowl Lip
Cowl ExteriorSupersonic External-Compression Inlet
L
EX
THSD
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Shock
Wave
Mach
Waves
NS
InletFlowfield
FreestreamApproach
FlowNose
External Supersonic
DiffuserCowl Lip
CowlExterior
ThroatSubsonicDiffuser
EngineFace
Station Description
0 Freestream
L Just upstream of the inlet
EX Just upstream of the normal shock
NS Just downstream of the normal shock
1 Entrance to interior duct at the cowl lip
TH Throat (minimum cross-sectional area)
SD Start of the subsonic diffuser
2 Engine face
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Freestream, Approach Flow, Engine Face
ML
D2 and
M2 or WC2
• Freestream conditions are known from aircraft mission (Mach number, altitude).
• The Approach Flow involves state changes (compression, expansion) due to flow over the
forward part of the aircraft. Station L has uniform flow just upstream of the start of the inlet.
• The Engine Face geometry and conditions (Mach number, corrected flow rate) are known as part
of the aircraft and propulsion system design process.
• Engine is a turbo-fan engine that typically operates at a constant corrected flow. For ML
approaching Mach 1.8, the engine may reach limits that reduce the corrected flow rate.
Freestream
& Approach
Flow
Engine
Face
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External Supersonic Diffuser
• An External Supersonic Diffuser is used for two-dimensional (Ktyp = 2 or 4) and axisymmetric
outward-turning (Ktyp = 3) inlets.
• The Nose is the leading edge (Ktyp = 2 or 4) or point (Ktyp = 3) of the external supersonic diffuser.
The nose can be sharp or round with a specified radius.
• The external supersonic diffuser consists of one or more stages through which compression
occurs through each stage by means of an attached shock wave or isentropic Mach waves.
• Shock and Mach waves pass through focal points (e.g. shock-on-lip).
Three-stage diffuser with smooth turning
Mach
Waves
ML
MEX
Three-stage diffuser with shock waves
External Supersonic
Diffuser
Cowl
Lip
Shock
Waves
Focal
Point
ML
MEX
• Design strategies emphasize minimizing total pressure loss
through the shocks and minimizing diffuser length while producing
the desired outflow Mach number (MEX).
• Two-dimensional diffusers include a sidewall to contain the
compression.
Sidewall
Diffuser
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External Supersonic Diffuser Types
• The factor Kexd controls the number of stages and design
methods.
Kexd = 1 & 2. Explicit specification of diffuser geometry
using , x, and y.
Kexd = 3. Explicit specification of diffuser geometry
using lines, NURBS curves, polynomials, or cubic
splines.
Kexd = 10. Single-stage ramp (2D) or cone (axi).
Kexd = 11. Two-stage ramp (2D) or bicone (axi).
Kexd = 12. Three-stage ramps (2D only).
Kexd = 13. Three-stages with second stage an isentropic
compression surface.
• For 2D ramps, a carpet search method is applied to
determine the ramp angles that result in the maximum total
pressure recovery for the diffuser (Oswatitsch condition).
• Conical flow solutions are determined using a numerical
solution to the Taylor-Maccoll equations.
• Bi-conic flow and isentropic diffuser contours are
determined using method-of-characteristics.
• Start and end of stages are determined by path of waves
and placement of the focal points.
Kexd = 10
Kexd = 11
Kexd = 13
External
Supersonic
Diffuser
pt2 / pt0 = 0.934
pt2 / pt0 = 0.949
pt2 / pt0 = 0.964
Relaxed External Compression
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Individually Distributed
Focal Points
• Start and end of stages are determined by path of waves
and placement of the focal points.
• May be desirable to alter focal points and wave angles to
provide greater margins of stability or tailor the flow.
• Two ways of relaxing:
1. Distribute the focal points for the waves.
2. Relax the angle of a downstream stage using Frelax.A value of F
relax= 0 would make downstream stage
the same angle as upstream stage.
Waves on the cowl lip
Frelax = 0.0
1 = 15o3 = 27.3o
1
3
Relaxed waves
Frelax = 0.5
1 = 15o3 = 21.1o
Cowl Lip
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• Cowl Lip coordinate yclip is specified or determined from
sizing operations. The code sets xclip = 0.
• Cowl Lip planar profile can be sharp, circular, or elliptical.
clex
clin
(x,y)clip
clexclin
(x,y)clip
Kclip = 1
Sharp
Kclip = 2
Circular
Cowl Exterior
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• Cowl Exterior provides an external surface for calculation of the wave drag.
• Geometry model creates baseline cowl exteriors based on factor Frcex, which
places the cowl exterior a multiple of the engine face radius.
• Axisymmetric cowl exteriors involve extruding a profile about the axis.
• Two-dimensional cowl exteriors involve building planar surfaces.
• Frontal area of cowl exterior influences cowl wave drag.
clex
(x,y)EF
rEF
rcext
(x,y)cext(x,y)cexm
(x,y)clex
ycexm = ycext
x
Kcex = 1
Cowl exterior model for two-dimensional inlets (Kdim = 2 or 4)
segment 1segment 2
clex(x,y)clex
(x,y)cexm
(x,y)cex1
(x,y)EF
(x,y)cex2(x,y)cext
rEF
rcext
ycexm = ycex2 = ycext
x
Kcex = 2
Cowl exterior model for axisymmetric inlets (Kdim = 1 or 3)
segment 1 segment 2 segment 3
Throat
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• Throat defines interior duct from stations 1 to SD.
• Station TH is the official “throat” station.
• The throat cross-sections follow the shape at station 1
(rectangular or axisymmetric).
• Throat area distribution is set by area ratios ATH / A1 and
ASD / ATH.
• For Kthrt = 2, the area ratio is calculated such that Mach
number MTH is established at station TH.
1 Subsonic
Diffuser
SD
TH
External
Supersonic
Diffuser
EXD1
CB1
CBSD
CWSD
CBTH
Cowl
Centerbody
(x,y)CBSD
(x,y)CWSD
(x,y)CBTH
CWTH
(x,y)CWTH
CB1 = EXD1 + CB1
(x,y)CW1 = (x,y)cwlin
(x,y)CB1 = (x,y)EXD1
CW1 = cwlin
Subsonic Diffuser
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• The subsonic diffuser transitions from the cross-section at
station SD to the cross-section at the engine face station 2.
• Two-dimensional inlets require transition from a rectangular
to a circular. Surfaces are created by the blending of
super-ellipses.
• Axisymmetric inlets are co-annular. Surfaces are created
by extruding profiles about the axis-of-symmetry.
• Geometric factors include key surface angles.
• Length of subsonic diffuser can be directly specified or
computed based on criteria of equivalent conical angle.
(x,y)EF
LCBX
(x,y)HEF
(x,y)TEF
(x,y)CBX
LSD
(x,y)CBSDCBSD
CWSD
SD
(x,y)CWSD
EF
CBX
Axisymmetric (Kdim = 3)
2-D
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Inlet Flow Rates
• Quantify W1, W2, Wspillage, Wbleed, Wbypass, etc…
• We know some flow rate information for the engine ( such as corrected flow, WC2 ).
• Flow rates should satisfy continuity through the inlet streamtube.
• Wcap is the theoretical capture flow rate.
• Inlet Flow Ratio = (W1 is the flow into the inlet)
• Three modes for external compression inletf low rates in supersonic flow:
o Subcritical (inlet flow ratio < 1, normal shock ahead of cowl lip)
o Critical (inlet flow ratio = 1, normal shock at the cowl lip)
o Supercritical (inlet flow ratio = 1, normal shock within the internal duct)
• Spillage is defined as
• Engine Flow Ratio =
cap
other
cap
jets
cap
bypass
cap
bleed
cap
spillage
cap W
W
W
W
W
W
W
W
W
W
W
W12
capW
W1
capcap
spillage
W
W
W
W11
capW
W2
Inlet Tools16
Inlet Total Pressure Recovery
• Inlet Total Pressure Recovery =
• Recovery is computed as increments through the inlet,
• Total pressure losses modeled within SUPIN:
o Normal, oblique, and conical shock waves
o Viscous diffusion supersonically or subsonically
o Sharp lip losses at high inlet flow rates at low
speeds (high inlet flow ratio)
• Inlet design objective is to maximize the total pressure
recovery.
• Characteristic cane curve relates the total pressure
recovery to the inlet flow ratio or engine flow ratio.
tL
t
p
p 2
0.75
0.76
0.77
0.78
0.79
0.80
0.81
0.82
0.85 0.90 0.95 1.00
pt 2 /
pt L
W2 / Wcap
line of
constant
WC
subcritical
super-
critical
increasing WC
buzz limit
critical
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Inlet Drag
• Inlet drag consists of those drag components that can vary with inlet flow rate.
• Inlet drag components:
• Spillage Drag ( Additive drag + Cowl lip suction)
• Cowl Drag ( Cowl lip drag + Wave drag)
• Bleed and bypass drag
• Additive drag is the sum of axial pressure forces acting on the streamtube ahead of the cowl lip.
• Cowl lip suction accounts for positive force due to acceleration of flow around a blunt cowl lip.
• Wave drag is the sum of axial pressure forces on the cowl exterior caused by supersonic flow.
• Bleed and bypass drag are the result of the loss of momentum of airflow through bleed and
bypass systems.
• Analytical and empirical methods are used to estimate drag components.Afcex
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Inlet Sizing
• Inlet sizing establishes the inlet dimensions
(Acap, LSD, Lexd, A1, ATH, ASD, angles, etc…)
• Sizing enforces the flow rate balance through the
inlet, and so, establishes the actual flow rates
(W1, W2).
• Sizing uses the total pressure recovery, which is
dependent on the sizing of the inlet. Thus an
iteration is involved that starts with an estimate
of the recovery that is improved with successive
iterations.
• Within SUPIN, the iteration is performed by
successive executions of SUPIN. With each
iteration, the input data file is updated with the
geometry properties and the total pressure
recovery.
cap
other
cap
jets
cap
bypass
cap
bleed
cap
spillage
cap W
W
W
W
W
W
W
W
W
W
W
W12
ref
ref
tt
tt
CTT
ppWW
2
2
22
121
2
2
21
2
2
22
11 M
RM
T
ApW
ref
ref
t
t
C
LLL
cap
capaM
WA
ML, L, aL, aL, M2
M2, A2, Tt2
cap
other
cap
jets
cap
bypass
cap
bleed
cap
spillage
W
W
W
W
W
W
W
W
W
W,,,,
Update pt2 through analysis
of inlet performance.
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Inlet Design Study
• Apply SUPIN to design a set of baseline inlets.
• M0 = 1.8, halt = 45000 ft., M2 = 0.5, D2 = 3.5 ft.
• Sharp nose. Three stages for the external supersonic diffuser (Kexd = 13).
MEX = 1.3. Shock-on-lip. Sharp cowl lip. Equivalent conical angle for the
subsonic diffuser = 3o.
• Conclusions:
o Pitot inlet does not perform well.
o Flow rate (W2) increases with higher total pressure recovery, but
essentially the same between 2D and axisymmetric external compression.
o Total pressure recovery is the same between 2D and axisymmetric
external compression.
o Two-dimensional bifurcated inlet is shortest inlet.
o Cowl external wave drag is significantly less for two-dimensional inlets.
Inlet W2 (slug/s) pt2/pt0 hclip (ft) L (ft) Acap (ft2) Afcex (ft
2) CDwave
Pitot 6.4330 0.8088 3.196 3.626 8.023 5.832 0.3313
2D 7.6450 0.9611 2.724 9.545 9.534 2.191 0.0947
Axisym 7.6665 0.9638 3.489 8.240 9.561 4.293 0.2233
Bifurcated 7.6455 0.9612 2.724 7.507 9.535 3.940 0.0852
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CFD Analyses
• SUPIN can create planar, structured, multi-block grid for 2D or
axisymmetric CFD.
• Use CFD methods (Wind-US) to solve planar flow field.
• Compute performance measures as a verification for SUPIN.
• 3D surface grids can be start to 3D grid generation.
Planar Grid
M0 = 1.8
Method W2 (slug/s) pt2/pt0 CDwave
SUPIN 6.4330 0.8088 0.3313
CFD 6.4039 0.8094 0.2764
Diff 0.45% -0.08% 16.55%
Method W2 (slug/s) pt2/pt0 CDwave
SUPIN 7.6665 0.9638 0.2233
CFD 7.2946 0.9317 0.1706
Diff 4.85% 3.34% 23.58%
Axisymmetric, Pitot Inlet (Ktyp = 1 ) Axisymmetric, O-T Inlet (Ktyp = 3 )
Future Plans
• Initial releases (March 2011):
– SUPIN as a beta test code
– Inlet Tools eRoom
– Inlet Design and Analysis Document (review draft)
• Continue the development of SUPIN:
– Enhance off-design performance analysis capability (Kmode = 3).
– Develop capability for design and analysis of internal and mixed-
compression inlets.
– Incorporate variable-geometry elements.
– Develop capability for design and analysis of three-dimensional or stream-
traced inlets.
– Incorporate quasi-one-dimensional CFD methods.
• Explore other programming options and platforms (Java).
• Explore partnerships with other researchers and organizations to
document and develop inlet tools.
• Contact: [email protected] (216) 433-8513
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Cruise Configuration
Subsonic Configuration
22Your Title Here 22